1. Field of the Invention
The invention relates to medicament pumps implantable in a body and more specifically to a device for filling high pressure reservoirs in medicament pumps implantable in a body.
2. Description of the Related Art
The implantable drug infusion pump (IDIP) has provided physicians with a powerful tool for administering a wide variety of drugs and other agents, such as pain killers, nerve growth factor, and anti-spasticity drugs, to very particularized sites within a patient""s body, such as the intrathecal region of the spinal column. The IDIP has also freed some patients from the restrictions of typical intravenous drug infusion systems that typically include a wheeled cart that must be pulled around behind the patient.
An IDIP is ordinarily surgically implanted subcutaneously in the patient""s abdomen. The IDIP has an internal reservoir for storing the drug or agent. After implantation, the drug or agent is delivered to a selected site in the patient""s body via a catheter that is attached to the pump and tunneled subcutaneously to the selected site. Many medical applications calling for an IDIP require very minute do sages or drug or agent to be delivered to the selected site over a period of time. For example, dosages of 100 xcexcl over a span of twenty-four hours are not uncommon.
Before the IDIP can be implanted in the patient""s body, it must be filled with the applicable drug or agent. For many long-term applications, the IDIP may have to be refilled while the pump is still implanted within the patient""s body. This is normally done by passing the drug or agent through a hypodermic needle that has been pierced through the patient""s skin and coupled to the subcutaneously disposed IDIP.
A prior art system for refilling and IDIP is shown in FIG. 1. The prior art system 10 includes a pharmacy syringe 12, a filter 14, a filling tube 16, and an IDIP 18. Filter 14 has an inlet 20 that is coupled to the discharge outlet 22 of the pharmacy syringe 12. Filter 14 is preferably any of a number of well known types that prevent bacteria, sediments or other undesirable particles from passing through it and into the IDIP 18.
The discharge orifice 24 of the filter 14 is coupled to the inlet end 26 of the filling tube 16. The filling tube 16 terminates in a needle 28. Pharmacy syringe 12 has a plunger 30. As the plunger 30 of the pharmacy syringe 12 is depressed, drug flows from the pharmacy syringe 12 through the filter 14 and the filling tube 16 and into the IDIP 18.
As shown in FIG. 2, the needle 28 enters the IDIP 18 through a septum 32. Septum 32 provides a fluid barrier for a chamber 34 within IDIP 18. Chamber 34 is fluidly connected to a reservoir 36 through a manifold 38. Reservoir 36 is typically formed within a bellows structure 40 that is connected to manifold 38. An outer shell 42 is attached to the manifold 38 around the bellows structure 40. A sealed pressure chamber 44 is formed between outer shell 42 and bellows structure 40.
A propellant gas is place in pressure chamber 44. The propellant gas acts as a pressure-providing means to the bellows structure 40 that biases the bellows structure 40 to discharge the drug or other agent stored in the reservoir 36. The propellant gas used to drive such a xe2x80x9cgas drivenxe2x80x9d IDIP is a fluid that is in phase change between a liquid state and a gas state when, i.e., in equilibrium between phases at around 37 degrees (Celsius), which is the usual temperature of the human body. In programmable IDIPs such as the SynchroMed pump manufactured and sold by Medtronic, Inc. of Minneapolis, Minn., the propeulant gas is chosen to provide a pressure on the bellows structure of about 4 p.s.i. In this device, the metering of the drug or other agent out of the device is done through a peristaltic mechanism.
In constant rate IDIPs such as the IsoMed(copyright) pump manufactured and sold by Medtronic, Inc. of Minneapolis, Minn., the propellant gas is chosen to provide a pressure on the bellows structure of about 32 p.s.i. In this device, the metering of the drug or other agent is done through capillary tube that provides a relatively constant flow rate of drug or other agent out of the reservoir 36. The reason for a higher pressure in the pressure chamber 44 in a constant rate pump with a capillary tube flow restrictor is that this higher pressure reduces the variability in flow rates of the drug or other agent due to atmospheric conditions such as barometric pressure.
As mentioned above, when refilling the IDIP, the drug or other agent is passed from a pharmacy syringe 12 through the filter 14 and the filling tube 16 and into the IDIP 18 where it passes into the reservoir 36. However, the drug or other agent must enter the reservoir 36 at a pressure sufficient to overcome the pressure bias on the reservoir 36 from the propellant gas in the pressure chamber 44. In the case of the IsoMed(copyright) pump, the drug or other agent must be delivered to the reservoir 36 at a pressure higher than 32 p.s.i.
Due to the principles of hydraulics, this 32 p.s.i. pressure is applied over the entire cross-sectional area of the plunger 30. When refilling an IDIP 18, typically the entire reservoir capacity of the IDIP is refilled. A typical IDIP 18 may have a reservoir volume of 20 ml, 40 ml or 60 ml. To refill an IDIP 18 with, for example, a 60 ml reservoir, a pharmacy typically prepares 60 ml of the drug or other agent and places it in a pharmacy syringe 12 corresponding in size to the amount of drug or other agent to be refilled, in this case, a 60 ml syringe. The 60 ml pharmacy syringe 12 could be coupled directly to the system 10 through the coupling of discharge outlet 22 and inlet 20.
As is well known, the cross-sectional area of the plunger 30 of a relatively small syringe such as a 10 ml syringe is smaller than the cross-sectional area of a larger syringe such as a 60 ml syringe. As a result, the force needed to apply 32 p.s.i. to drug or other agent in a pharmacy syringe 12 is determined by multiplying 32 p.s.i. by the crosssectional area of the plunger 30. In the case of a 60 ml syringe, this total force is on the order of 25 pounds. This is a larger force than many people are able to generate with their hands. On the other hand, because the cross-sectional area of a 10 ml syringe is about a quarter of the cross-sectional area of a 60 ml syringe, the total force needed to apply apply 32 p.s.i. to drug or other agent in a pharmacy syringe 12 is about 6 pounds. This force is well within the range of force that most people can generate with their hands.
As a result, many practioners, when refilling large reservoir pumps such as the 60 ml reservoir pumps, require the pharmacy to place the 60 ml of the drug or other agent to be refilled into several smaller syringes such as 10 or 20 ml syringes instead of in one large syringe. These smaller syringes allow the practioner to apply the drug or other agent to the reservoir 36 even in pumps such as the IsoMed(copyright) pump that have relatively high gas propellant pressures in the pressure chambers 44. Unfortunately, using several smaller syringes instead of one large syringe means that each pharmacy syringe 12 must be attached and disconnected from the inlet 20 each time instead of once as would be the case for the larger syringe. With this increased number of connections and disconnections, there is an increased chance of infection entering the system or other problems occurring.
In view of the foregoing, it is desirable to provide a system that allows the practioner to easily provide the drug or other agent to the reservoir 36 of the IDIP 18 while at the same time minimizing the number of times the sterile connection between the pharmacy syringe 12 and the system 10 is broken. The present invention is directed to overcoming the aforementioned disadvantage. Throughout this disclosure, like elements, wherever referred to are referenced by like reference numbers.
A device and method for aseptically filling high pressure reservoirs in medicament pumps is disclosed. The device preferably includes a filter, a connector having a one-way valve and a filling tube with a terminal needle. The filter is connectable to a pharmacy prepared syringe containing the drug or other agent to be transferred to the reservoir of the IDIP. The filter is in turn connected to the connector.
The connector has a first and a second inlet port and an outlet port. The two inlet ports are fluidly connected to the outlet port. The first inlet port is connectable to the pharmacy syringe containing the drug or other agent to be transferred to the reservoir of the IDIP. The second inlet port is connectable to a filling syringe. The filling syringe is preferably of a size that allows the practioner to easily apply sufficient force to the drug or other agent to overcome the pressure bias on the reservoir of the IDIP and allow the drug or other agent to be admitted to the reservoir to refill the reservoir.
A one-way valve is located in the connector xe2x80x9cupstreamxe2x80x9d of the point where the two inlet ports connect to the outlet port on the first inlet port leg of the connector. The one-way valve allows fluid to flow from this syringe to either the second inlet port or the outlet port. But, the one-way valve prevents fluid from flowing from either the second inlet port or the outlet port through the first inlet port. The filling tube is connectable to the outlet port.
In use, a syringe containing the drug or other medicament to re-fill the IDIP is connected to the first inlet port. A filling syringe is connected to the second inlet port. The filling tube is connected to the outlet port. The terminal needle of the filling tube is passed through the patient""s skin and through the septum of the IDIP where the drug or other agent may pass into the chamber and ultimately into the reservoir of the IDIP.
The practioner draws the drug or other agent into the filling syringe from the pharmacy prepared syringe by pulling the plunger of the filling syringe back. This causes drug in the pharmacy prepared syringe to move from the pharmacy prepared syringe through the one-way valve through the connector to the filling syringe. When the filling syringe is full, the practioner pushes the filling syringe plunger in thereby forcing the drug or other agent out of the outlet port, through the filling tube and terminal needle into the chamber of the IDIP and ultimately into the reservoir of the IDIP. The one-way valve prevents the drug or other agent from re-entering the pharmacy prepared syringe. Since the filling syringe is typically smaller than the pharmacy prepared syringe, several cycles of filling and emptying the filling syringe as described above will need to be performed in order to transfer the drug or other agent from the pharmacy prepared syringe to the reservoir of the IDIP.